User guide

VMP 18” variable mass passive-radiator
Fix and Variable Parameters
Parameter
15" VMP
Description
Qms
7
Mechanical Q
Cms
71
um/N, compliance
Dia
390
m meters, effective
Mms (Range)
690 – 2460
grams, effective mass
Fs (Range)
22 – 11.9
Hertz, Free Air Resonance
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Empty
Nut
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18
Mass (washers)
Resonance Frequency
Directions for Use
VMP’s are designed to supplement ports in bass-reflex systems. The TC Sounds VMP can be tuned lower by adding
mass washers or higher by removing them from the adaptor under the cone. Adding additional VMP’s is equivalent to
increasing the port diameter in a ported system, and adding mass to a VMP is equivalent to increasing a port’s length.
Adding a second VMP to the system effectively raises the net tuning and additional mass must be added to both
VMP’s to maintain the same system tuning frequency as opposed to using just one VMP. Additional VMP’s increases
the resonator’s headroom and allows the subwoofer to push more air before compression. Ideally two same-sized
VMP’s should be used with one active driver, but TC VMP’s can be utilized on a 1:1 ratio in small box systems with
good results. If only one VMP is used, the subwoofer may be subject to shaking due to mass imbalance. This does not
have any sonic problems, but fastening the enclosure may be necessary. Two opposing VMP’s will mass-cancel and
eliminate shaking.
The above graph shows the free-air resonances of a VMP as additional mass-washers are added. For modeling a
passive radiator system with a VMP, use any Fs number from the graph you like in addition to the fixed Cms, Qms
and Cone Diameter above. Note that during the first few uses, the VMP will break in and the compliance will increase
therefore lowering the effective Fs.